The present invention relates to measurement techniques of sensitive microwave circuits, such as quantum superconducting circuits, which require protection from infrared radiation in a certain bandwidth without degrading the signal to noise ratio of the microwave signals feeding or measuring these circuits, and more specifically, relates to a low-loss infrared filter implemented as a distributed Bragg reflector in a microwave transmission line, e.g., of a stripline geometry.
In one approach called circuit quantum electrodynamics, quantum computing employs active superconducting devices called qubits to manipulate and store quantum information, and resonators (e.g., as a two-dimensional (2D) planar waveguide or as a three-dimensional (3D) microwave cavity) to read out and facilitate interaction among qubits. As one example, each superconducting qubit may comprise one or more Josephson junctions shunted by capacitors in parallel with the junctions. The qubits are capacitively or inductively coupled to 2D or 3D microwave cavities. The electromagnetic energy associated with the qubit is stored in the Josephson junctions and in the capacitive and inductance elements forming the qubit. To date, a major focus has been on improving lifetimes of the qubits in order to allow calculations (i.e., manipulation and readout) to take place before the information is lost due to decoherence of the qubits. Currently, the coherence times of superconducting qubits can be as high as 100 microseconds, and efforts are being made to increase their coherence times.